Hydrostatic transmission and controls

ABSTRACT

A hydrostatic transmission, especially for a steer drive of a propulsion and steer drive transmission, having a variable displacement pump, a fixed displacement motor, and a pump displacement control, and including a low pressure fluid source supplying the charging and lubrication systems of the hydrostatic transmission and a high pressure source. The high pressure source, in a normal range of low hydrostatic power pressure values, provides control pressure regulated in proportion to high hydrostatic power pressure to meet the pressure requirements of the pump displacement control which increase with high hydrostatic power pressure. In an abnormal and lower range of low hydrostatic pressure values, the control pressure is regulated to decrease to zero as the low hydrostatic power pressure decreases to a minimum operating pressure value. In the abnormal range, the reduction of control pressure reduces load capacity and thus steer capacity, with decreasing low pressure supplied to the charging and lubrication systems to advise the operator of the abnormal pressures and to discontinue hydrostatic transmission operation to prevent operation with insufficient charging and lubrication pressures.

FIELD OF THE INVENTION

The invention herein described was made in the course of work performedunder a contract or subcontract thereunder with the United StatesDepartment of the Army.

This invention relates to hydrostatic transmissions and a control systemtherefor and, more particularly, to a control system having a lowpressure source to supply fluid to the lubrication and charging systems,and a high pressure control system.

RELATED APPLICATION

U.S. Application Ser. No. 051,110 filed June 22, 1979 in the names ofMax E. Stewart and James R. Lucas, by the common assignee, is related.

BACKGROUND OF THE INVENTION

This invention provides an improved hydrostatic transmission and controlsystem, preferably for use in a radial piston-type hydrostatictransmission as shown in U.S. Pat. No. 3,274,946 Simmons, granted Sept.27, 1966, and U.S. Pat. No. 3,752,010 Tipping, granted Aug. 14, 1973;and also may be used in hydromechanical transmissions, as shown in U.S.Pat. No. 3,982,448 Polak et al, granted Sept. 28, 1976; and incross-drive transmissions having a hydrostatic steer drive transmissionunit, such as in U.S. Pat. No. 3,373,636 Livezey et al, granted Mar. 19,1968, and U.S. Pat. No. 3,640,157 Schaefer, granted Feb. 8, 1972.Related hydrostatic transmission controls are shown in the above U.S.Pat. No. 3,640,157.

SUMMARY OF THE INVENTION

This invention provides an improved control system for hydrostatictransmissions of the variable displacement type having hydrostatic pumpand motor units. One or both of the pump and motor units has variabledisplacement controls so that the relative displacement of these unitsmay be varied to vary the torque ratio. Preferably a variabledisplacement pump is used with a fixed displacement motor, and both pumpand motor units are radial piston units, with a plurality of sphericalpistons fixed on the rotor, and a cylinder reciprocally mounted on eachpiston and supported by a slipper bearing on a bearing ring.

The variable displacement controls have a displacement control membermovable from a null position providing zero displacement of thecontrolled pump through increasing displacement positions to increasethe displacement of the controlled pump. In these displacementpositions, the high hydrostatic power pressure or load on the controlledpump provides a proportional reaction force on the displacement controlmember tending to return it to the null position. The displacementcontrols provide a displacement control force proportional to the highhydrostatic power pressure to position the displacement control memberfor drive operation. In the pump, this inherent reaction force tends tomove the bearing ring to the null position, and the force required tomove the bearing ring to increase displacement is proportional tohydrostatic power pressure or load which normally is proportional todisplacement, the degree of steer demand, and steer conditions.

The control system has a low pressure system including a low pressuresupply for supplying low pressure fluid to an operation support systemhaving a charging system using low pressure fluid to charge thehydrostatic power transfer passage system of the hydrostatictransmission, the lubrication system employing low pressure fluid forlubrication, and the high pressure pump of the high control pressuresystem which receives low pressure fluid and supplies high controlpressure for controlling the displacement of the hydrostatic pump.

The displacement control system has a displacement or manual steercontrol valve selectively connecting high control pressure to thedisplacement control fluid motor device to control the position of thedisplacement control member or bearing ring to control pumpdisplacement. The high control pressure supplied by the high pressurepump is regulated by a primary regulator valve in a normal pressurerange in proportion to load by the high hydrostatic pressure to meet theforce requirements for positioning the displacement control member, withlow parasitic power loss. The high control pressure is regulated byconnecting overage fluid flow to the low pressure system to supplementthe low pressure source to normally provide a supply flow capacitymeeting operation support system flow requirements at a normal regulatedlow pressure value regulated by a downstream regulator valve in thesource to reduce parasitic power loss. During abnormal operation, whensupply flow capacity of the low pressure supply does not meet flowrequirements of the operation support system, e.g., due to excessleakage, the low pressure value decreases.

The high control pressure is reduced from the normal value proportionalto high hydrostatic power pressure and load when the charging or lowhydrostatic power pressure or low supply pressure decreases below anormal pressure range. This normal pressure range of the low pressuresource extends from the normal regulated low pressure, down to a minimumnormal low pressure value, to include any normal transient pressurevariations. Thus, in this normal pressure range the low pressure fluidsupply is sufficient for proper supply and full power operation of thehydrostatic transmission, including the operation support system, thecharging and lubrication systems, and the high pressure pump.

When low pressure decreases below the normal pressure range through anabnormal low pressure range to a minimum operating pressure valuesufficient for proper hydrostatic transmission operation, the highcontrol pressure is proportionally reduced to zero. This reduction ofhigh control pressure reduces or limits the capacity of the displacementcontrol to control displacement to provide higher hydrostatic powerpressures, so the high hydrostatic power pressure and thus torque loadcapacity for drive are both reduced or limited. This reduction of highhydrostatic power pressure reduces the pressure and flow requirements ofthe low pressure supply for proper operation of the operation supportsystem of the hydrostatic transmission. When the hydrostatictransmission provides the steer drive of a propulsion and steer drivetransmission, the reduction of available high hydrostatic power pressureand thus load capacity causes a resultant degradation of steercapability, such as limiting steering to larger radius turns, to advisethe operator that he is exceeding steering capabilities and that lowsupply pressure has decreased to the abnormal range. The reduction ofhigh hydrostatic power pressure will reduce the leakage, the torqueload, and bearing loads and provide a reduction of the heating effectand the temperature of the fluid. When the reduction of low pressure isdue to excessive steer demand, operation at reduced high hydrostaticpower pressure will effect cooling and reduce leakage to increase lowhydrostatic power pressure to the normal range for normal operation.When the reduction of low hydrostatic power pressure continues andindicates a need for service, the operator, during a gradual reductionof low hydrostatic power pressure, has limited steer capacity forvehicle retrieval.

The high control pressure regulator connects overage fluid flow tosupplement the low pressure fluid supply which normally is provided by aregulated low pressure source, a pump and regulator valve. In thepreferred arrangement, the high mainline or primary regulator valveconnects overage fluid flow to supplement the low pressure supply. Thisoverage fluid flow supply is increased when the displacement controlpressure is reduced by the blocking action of the secondary regulatorvalve in response to abnormal low hydrostatic power pressure, so thereis increased fluid flow tending to increase low hydrostatic powerpressure from the lower pressure abnormal range to the higher pressurenormal range. In the modified arrangement, the primary regulator valvewill provide overage fluid flow only in the normal range, and thesecondary regulator valve provides overage fluid flow in the abnormalrange. Further decrease of the low hydrostatic power pressure to valuesresulting in a low pressure supply having a pressure less than theabnormal range and inadequate for proper charging and lubricationdiscontinues control pressure providing zero or null displacement toabort or discontinue transmission steer drive operation and direct allflow to the low pressure supply.

These and other features of the invention will be more apparent from theaccompanying drawings and the following description of the preferredembodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial sectional view of the hydrostatic transmission,mainly on the line 1--1 of FIG. 2.

FIG. 2 is a reduced partial cross section of FIG. 1, on the line 2--2.

FIG. 3 is an enlarged partial section of FIG. 2, on the line 3--3.

FIG. 4 is a reduced partial sectional view of FIG. 2, on the line 4--4,showing the pump ring pivot.

FIG. 5 is a view of the pump cylinder from the slipper bearing end.

FIG. 6 is a side view of FIG. 5 on line 6--6.

FIG. 7 is an enlarged partial sectional view of FIG. 5, on the line7--7.

FIG. 8 is a plot of balancing pressure gradient curves across the widthof the bearing surface.

FIG. 9 is a view of the motor cylinder like FIG. 5.

FIG. 10 is an enlarged sectional view of FIG. 9, on the line 10--10.

FIG. 11 is a schematic view of the control system and lubrication supplysystem.

FIG. 12 is a partial sectional view, with parts broken away, of thesteer valve, on line 12--12 of FIG. 11.

FIG. 13 is a schematic view of a modified secondary regulator valve.

DESCRIPTION OF PREFERRED EMBODIMENT

FIGS. 1 and 2 show a structural arrangement of the hydrostatictransmission 10. Transmission 10 has a housing 11 having a partialbarrel portion 12, an input end wall 13 and an output end wall 14.Central support wall 16 is secured to housing 11 by a plurality ofscrews 15 fastened to ears 15' on barrel portion 12 of housing 11,spaced around the perimeter of central support wall 16--one screw 15 andone ear 15' being shown in FIG. 2. Central support wall 16 has acircular opening 17 formed therein to receive the support cylinder 18 ofthe pintle 19 which supports the pump 23 and motor 23' of hydrostatictransmission 10. A securing flange 21, on the end of support cylinder18, is secured by fasteners 22 to the support wall 16 to fix pintle 19to central support 16 fixed in housng 11. In pintle 19, support cylinder18, smaller diameter cylindrical pump bearing 28, and motor bearing 28',and pintle end portion 19', are centered on pintle axis (P). Pintle endportion 19' may be used to provide fluid connections (not shown) fromthis hydrostatic transmission 10, when used for steer-drive, to otherportions of a propulsion and steer-drive transmission in which thishydrostatic transmission may be used as the steer-drive.

Pump 23 has a rotor 24 with a sleeve portion 25 having drive spline 26,and an internal bearing 27 rotatably mounted on cylindrical pump bearing28 on pintle 19. There is a step 20 between the larger diameter supportcylinder 18 and smaller diameter cylindrical pump bearing 28. Pump rotor24 also has piston members 29 (preferably nine), each having a tubularsupport portion 31 secured at one end, preferably by threads, to sleeveportion 25 in rotor port 32, and each having a through-passage 33aligned with rotor port 32. Each piston member 29 also has an annularpiston portion 34 formed integrally with or fixed on the distal end ofeach tubular support portion 31. Each annular piston portion 34 has anexternal spherical surface 36, annular in extent, contacting the innercylindrical surface 37 of cylinder portion 38 of cylinder member 39, andcooperating with each piston member 29. Each cylinder member 39 has aslipper bearing 41, formed integrally with or secured to cylinderportion 38, to close the radially outer end of the cylinder portion 38and provide a cylinder chamber 42 between piston member 29 and cylindermember 39. Each slipper bearing 41 has a cylindrical slipper bearingsurface 43 engaging the cylindrical internal bearing surface 44 of pumpbearing ring 46, constructed as described below with reference to FIGS.5 to 7, to provide a hybrid bearing 45 having a hydrostatic bearingcomponent 138 and a hydrodynamic bearing component 139. Annular dams 47are secured by a plurality of fasteners 48 to each side of the pumpbearing ring 46 and project radially inwardly a short distance, aboutequal to the thickness of the slipper bearing 41, beyond internalbearing surface 44 to retain fluid on internal bearing surface 44 forlubrication. Each annular dam 47 has an annular recess 49 formed thereinfor receiving guides 50, one at each end on each side, and of matchingcircular shape on the slipper bearing 41 of cylinder member 39 (bestshown in FIGS. 5 and 6), to mechanically position the cylinder member 39near operating position so the fluid pressure and centrifugal forcesduring operation will move slipper bearing 41 radially, without canting,into contact with pump bearing ring 46. An annular stop member 51 issecured by screws 52 to annular step surface 53 of pintle 19 betweenpump bearing 28 and pintle end portion 19' to retain thrust bearing 54on one side of pump rotor 24. Thrust bearing 55 is located at the otherside, between pump rotor 24 and the step 20, to axially locate pumprotor 24.

Fixed displacement motor 23' has the same structure as pump 23, exceptas pointed out below, so like reference numerals (primed) have beenapplied to the parts of motor 23' which are like the above-describedparts of pump 23 and pintle 19, and reference is made to the abovedescription of pump 23. Motor 23' includes a motor bearing 28' on pintle19, a motor rotor 24' having a sleeve portion 25' rotatably mounted onmotor bearing 28', and piston members 29' slidable in cylinder members39', each having a slipper bearing 41' with a slipper bearing surface43' engaging the internal bearing surface 44' of motor bearing ring 46'.

The pivotal mounting of pump bearing ring 46 to vary displacement ofpump 23 and the fixed mounting of motor bearing ring 46' of fixeddisplacement motor 23' are described below. The differences between thepump and motor slipper bearing surfaces 43 and 43' of slipper bearings41 and 41' are described below, with reference to FIGS. 5 to 11.

Central support wall 16 has, on the pump side, a pump clearance recess56 with an outer diameter 57 concentric with axis (P) of pintle 19, andsufficiently large so as to provide clearance for the adjacent annulardam 47 on pump bearing ring 46 to permit displacement-varying movementof pump bearing ring 46 in opposite directions from the null position onthe null axis (N), as shown in FIG. 2 and hereinafter described. Centralsupport wall 16 has, on the motor side, motor clearance recess 56'having an outer diameter 57' concentric with motor axis (M), FIG. 2, toprovide clearance for the adjacent dam 47' on fixed motor bearing ring46'.

The pump bearing ring 46 is pivotally supported by a pin 58 located inbores 59 and 60 respectively in central support wall 16 and pump bearingring 46 (FIGS. 2 and 4). A circular key 61, fitting a circular keyway inpin 58 and secured by screw 62 to support wall 16, fixes pin 58 tosupport wall 16. A circular retainer plate 63, secured by screws 64 tothe opposite end of pin 58, retains pump bearing ring 46 on pin 58against support wall 16 for pivotal movement about pivot axis (A) of pin58 to vary pump displacement. Presently a headed pin and retainer plate63 (not shown) is used. Pump bearing ring 46 (FIG. 2) is shown on thenull axis (N) extending through pivot axis (A) and pintle axis (P)which, in null position (N) is also the pump null axis, or zero strokeor displacement axis.

At the opposite end on the other side of pintle 19, pump bearing ring 46(FIGS. 1, 2, and 11), has a cross-slot 66 perpendicular to the null axis(N). Connecting rods 67 and 68 respectively are pivotally connected bypins 69 and 71 to pump bearing ring 46 and connected by ball and socketjoints to pistons 72 and 73 reciprocally mounted in cylinders 74 and 76of fluid motors 77 and 78. A support bracket 79 has a central portion 81secured by screws 82 to the transverse flat end 83 of central supportwall 16 and has, at opposite ends thereof, ears 84 and 86 projectinglaterally from and secured respectively to cylinders 74 and 76 tosupport right and left fluid motors 77 and 78 in alignment with pumpbearing ring 46.

Motor bearing ring 46' is fixed by two locating dowels 87 and aplurality of screws 88 fastened to central support wall 16 to provide afixed displacement motor 23'.

At the input end of housing 11 there is an engine driven input drive 91having a drive gear 92 driving transmission input gear 93 locatedbetween input end wall 13 and inner input end wall 94. Screws 95 secureinner input end wall 94 to input end wall 13. Input gear 93 has a sleevehub portion 96 at its inner diameter. Bearings 97 and 98 are fixed inapertures 101 and 102 respectively in input end wall 13 and inner inputend wall 94 and are fixed on the outer diameter of sleeve portion 96 onopposite sides of input gear 93 to rotatably support input gear 93.Apertures 101 and 102 may have steel rings 99 press-fitted into theseapertures if housing 11 is made of aluminum. Input gear 93 is driveconnected, through sleeve hub portion 96 and its internal splines 103,to splined sleeve shaft 104 employed to drive other components of thetransmission, such as a propulsion transmission (not shown), and to pumpsleeve shaft 108 by external splines 106 on small diameter portion 107of pump sleeve shaft 108. The large diameter portion 109 of pump sleeveshaft 108 is connected by internal splines 111 to drive spline 26 onsleeve portion 25 of pump rotor 24 to drive the pump rotor 24.

The motor rotor 24' has drive splines 26' drive connected to internalsplines 112 on large diameter portion 113 of motor sleeve shaft 114.Motor sleeve shaft 114 also has a small diameter portion 116 having asun gear 117. A plurality, preferably four, of planetary pinions 118 arerotatably mounted on a carrier 119 and mesh with sun gear 117 torotatably support motor sleeve shaft 114. Pinions 118 also mesh with thering gear 121 seated on an annular seat 122 on the output end wall 14and secured thereto by screws 123. The outboard side member 124 ofcarrier 119 is rotatably supported at its inner diameter by bearing 126mounted on output end wall 14. The inboard side member 127 of carrier119 has, extending radially outwardly therefrom, an output gear 128 andat a radially inner diameter, a sleeve portion 129 supported withinbearing 131 fixed in aperture 132 in inner output end wall 133, which issecured by screws 134 to output end wall 14. Output gear 128 drivesfinal output gear 136. A thrust bearing 137 is located between carrieroutboard side member 124 and small diameter portion 116 of motor sleeveshaft 114.

Each of the pump cylinder members 39 has a slipper bearing 41 having aslipper bearing surface 43 in bearing engagement with internal bearingsurface 44 and constructed, as shown in FIGS. 1 and 5 to 7, to providehybrid bearing 45 with a hydrostatic component 138 and a hydrodynamiccomponent 139. The cylinder chamber 42 in pump cylinder member 39 isconnected by a restricted port 141 centrally located in cylinder member39 and slipper bearing 41 to supply hydrostatic power fluid, which is alubricant, to a narrow distribution recess 142 extending in thedirection of rotation of cylinder member 39. Distribution recess 142 isin the form of a shallow narrow groove that extends about the fulllength of slipper bearing surface 43 and divides the bearing surface 43into two portions 143 and 144, one on each side of distribution recess142. Distribution recess 142 functions mainly as a lubricating fluiddistribution recess or passage and secondly as a balancing recessproviding a small portion of the balancing force. Slipper bearingsurface 43 and its portions 143 and 144 are cylindrical and have adiameter less than the cylindrical internal bearing surface 44 by thedesired journal bearing running clearance 145, e.g., 0.008 inch radialclearance. At the ends 146 and 147, one being a leading end and theother being a trailing end depending on the direction of rotation, ofthe bearing surface 43, tapers 148 and 149 begin and respectivelyenlarge toward edges 151 and 152, one leading and the other trailingduring rotation, of slipper bearing 41. During rotation of cylindermember 39 in the direction of rotation (arrow PR, FIG. 7), edge 151 isthe leading edge. At the leading edge, taper 148 and internal bearingsurface 44 form a wedge-shaped injection space 150 having an entranceportion 154 having a height substantially greater, e.g., about fivetimes, than the lubricating fluid film thickness. The lubricating fluidflows through the running clearance and exits via the taper 149 at thetrailing edge 152. In applications where the direction of rotation isreversed, edge 152 becomes the leading edge and taper 149 provides thesame type injection space. Distribution recess 142 has a base 153 havinga larger diameter than that of slipper bearing surface 43, so the depthof distribution recess 142 below the slipper bearing surface 43 is amaximum at the center at restricted port 141 to ensure free feed flow ofhydrostatic power fluid for lubrication to distribution recess 142, anddecreases to a minimum depth, substantially zero, at the opposite ends146 and 147 of bearing surface 43. The slipper bearing surface 43 isonly spaced from the internal bearing surface 44 by the thickness of thelubricating fluid film during operation, so distribution recess 142 isenclosed and functions as a fluid distribution passage substantiallyclosed at the sides and ends to maintain hydrostatic balancing fluid indistribution recess 142 substantially at the hydrostatic power pressurein cylinder chamber 42. The restricted port 141 has a very smalldiameter (e.g., 0.055 inch) and area (e.g., 0.0024 inch), while thedistribution recess has a much larger cross-sectional area (e.g., 0.0043inch), nearly double the area of restricted port 141, so the restrictedport at low load limits the hydrostatic power fluid flow for lubricationfrom cylinder chamber 42 to distribution recess 142 and there is freeflow in distribution recess 142. The hydrostatic power fluid indistribution recess 142 flows laterally to both sides to form alubricating fluid film between the slipper and internal bearing surfaces43 and 44. This hydrostatic power fluid supply for lubrication providesa hydrostatic balancing pressure gradient decreasing from substantiallyhydrostatic power pressure in distribution recess 142 at the center tozero at the opposite side edges to provide a hydrostatic balancepressure having an average value about one-half hydrostatic powerpressure in the absence of hydrodynamic balancing pressure. Thishydrostatic balancing pressure gradient has a transverse profile curveacross hybrid bearing 45 (Curve Hs, FIG. 8), for high hydrostatic powerpressure operation and similar curves with lower maximum pressures forlower hydrostatic power pressure operation. This hydrostatic balancingpressure acts on the area of the pump slipper bearing surface 43 andvaries with hydrostatic load to balance a high portion (90% to 95%), butnot all, of the hydrostatic load due to hydrostatic pressure acting onthe end area of cylinder chamber 42 at all hydrostatic pressure values.

When the direction of rotation of cylinder member 39 relative to pumpbearing ring 46 is such that edge 151 is the leading edge, the taper 148at leading edge 151 is effective to force lubricating fluid intoclearance 145 between the slipper and internal bearing surfaces 43 and44. The taper 148 forms a wedge injection space 150 completely acrossleading edge 151 having an entrance portion 154 having a heightsufficiently (preferably five times) greater than the fluid (oil) filmthickness to force-feed the lubricating fluid for longitudinal flowbetween slipper and internal bearing surfaces 43 and 44. Thishydrodynamic component 139 of the hybrid bearing 45 provideshydrodynamic lubricating fluid flow and balancing pressure proportionalto speed to balance the centrifugal load and the remainder of thehydrostatic load. The area and width of distribution recess 142 issmall, e.g., 7.5% of the area and width of slipper bearing surface 43,so the leading taper 148 and slipper bearing surface portions 143 and144 are effective over substantially all of the width and area ofslipper bearing surface 43 to provide hydrodynamic balancing pressureand fluid flow. In the absence of hydrostatic balancing pressure at highspeed, the hydrodynamic balancing pressure gradient has a transverseprofile curve across the hybrid bearing 45 (Curve Hd, FIG. 8) havingsimilar curve portions across each of slipper bearing surface portions143 and 144, with the pressure being maximum at the center anddecreasing to zero at the edges at the side and at the recess 142 forhigh speed operation. As speed decreases, the maximum hydrodynamicbalancing pressure decreases. The hydrodynamic balancing pressure coactswith or confines the hydrostatic balancing pressure to provide acombined or total balancing pressure having a transverse profile (CurveT) having a maximum pressure centrally of each slipper bearing surfaceportion 143, 144, and decreasing with the hydrostatic pressure gradientto zero at the side edge and to the hydrostatic pressure at recess 142.There is an additive effect of hydrostatic and hydrodynamic balancingpressure limited or reduced by the pressure gradients, so the averagetotal balancing pressure is larger than the average of either thehydrostatic or hydrodynamic balancing pressure.

Since pump 23, during low starting speed operation, always has only thesmall supercharge hydrostatic pressure load and no higher hydrostaticpower pressure load and no significant hydrodynamic load, thehydrodynamic component 139 is not functioning and the hydrostaticcomponent 138 functions to meet these lubrication requirements of hybridbearing 45. As pump speed is increased to the normal high running speed,hydrodynamic lubricant fluid flow and balancing pressure increase tomeet requirements. At high speed and minimum or charging to a lowhydrostatic power pressure, the hydrostatic pressure fed throughrestricted port 141 supplies hydrostatic lubricant fluid at a lowbalancing pressure only to balance the low hydrostatic load at a lowflow rate only sufficient for lubrication and cooling requirements atlow speed; and the leading taper 148 provides added hydrodynamiclubricant fluid flow and hydrodynamic balancing pressure to meet therequirements of the hydrodynamic load due to speed for a totallubricating fluid flow and balancing pressure meeting high speed and lowhydrostatic pressure lubricating requirements.

Hydrostatic pressure lubrication flow and balancing pressure at minimumhydrostatic pressure, unloaded at starting speeds, meets minimumhydrostatic or total lubrication requirements and, at higher runningspeeds, is insufficient to meet hydrostatic lubrication requirements. Ashydrostatic pressure increases at running speeds to a maximum, thehydrostatic pressure feed supplies hydrostatic lubricating fluid at aflow rate which tends to increase but is reduced or limited byhydrodynamic balancing pressure and decreasing clearance and at anincreasing hydrostatic balancing pressure to meet a large portion butnot all hydrostatic fluid flow and balancing pressure requirements. Athigh speed and minimum to maximum hydrostatic pressure, the hydrostaticpressure feed for lubrication has a low flow rate and supplies a minorportion of total fluid flow and balancing requirements, and hydrostaticbalancing fluid flow which increases with speed supplies a major portionof total balancing pressure and fluid flow requirements. Hydrodynamiclubricating fluid flow and balancing pressure supplement and limithydrostatic fluid flow and supplement hydrostatic balancing pressure tomeet total requirements as they vary with speed and load to minimizeslipper bearing area requirements and minimize the amount of hydrostaticpower pressure bled for lubrication and thus power loss over the fullrange of operation--especially at the critical maximum hydrostatic powerpressure.

The motor hybrid bearings 45' shown in FIGS. 1, 9, and 10, are similarto the above-described pump hybrid bearings 45, so like referencenumerals (primed) have been used with reference to the above descriptionfor like parts and features, and to the following description of thedifferent parts and features. Motor slipper bearing surface 43' engagesinternal bearing surface 44' of motor bearing ring 46' to provide motorhybrid bearing 45'. Motor cylinder chamber 42' is connected by centrallylocated restricted port 141' to a distribution recess 142' which is asquare recess centrally located in the cylindrical slipper bearingsurface 43'. The base 153' of distribution recess 142' is substantiallyflat so the depth of the recess at the center at restricted port 141' issufficient for free fluid flow from restricted port 141' to distributionrecess 142'. Motor slipper bearing surface 43' has similar ends 146' and147', tapers 148' and 149', and edges 151' and 152'.

In motor 23' hydrostatic balancing pressure acts on the area ofdistribution recess 142' and has a hydrostatic pressure gradientdecreasing from hydrostatic power pressure at recess 142' to zero at theedges of slipper bearing surface 43'. This decreasing pressure gradienthas an average value about one-half of hydrostatic pressure acting onthe net area of slipper bearing surface 43' (the area of slipper bearingsurface 43' minus the area of recess 142'). Thus, motor hydrostaticbalancing pressure curve profile is similar to that of pump 23 (CurveHs), but hydrostatic pressure extends across the wider recess 142' andacts on a larger area, so average motor hydrostatic balancing pressureis higher in relation to hydrostatic power pressure than average pumphydrostatic balancing pressure. The hydrostatic balancing force providedby hydrostatic balancing pressure acting on the full area of motorslipper bearing surface 43' is equal to all (100%) of the hydrostaticload through the full range of hydrostatic power pressure acting on theend area of motor cylinder chamber 42' at lower starting speeds, and isa high portion (90% to 95%), but not all, of the hydrostatic load duringhigher running speed operation. The restricted port 141' is small (e.g.,0.055 in.) to provide a rate of flow and amount of lubricating fluidincreasing with hydrostatic pressure just meeting bearing fluid flowrate requirements as hydrostatic pressure increases at low startingspeeds. As speed increases in one direction so edge 151' is the leadingedge, the taper 148' injects lubricating fluid into running clearance145' between slipper bearing surface 43' and internal bearing ringsurface 44' to increase lubricating fluid flow to meet lubricating fluidflow requirements of hybrid bearing 45' which increase with speed. Themotor hydrodynamic balancing profile is like that of the pump (CurveHd), but basically extends only over the smaller width and area ofslipper bearing surface 43' between recess 142' and the side edges, andthus has a smaller average pressure acting on a smaller area than in thepump.

Motor hydrodynamic balancing pressure confines and additively coactswith motor hydrostatic balancing pressure, as in the pump, to provide alarger total balancing pressure. Since the area of the squaredistribution recess 142' is about twice that of the narrow groove-typedistribution recess 142, motor slipper bearing 41' provides morebalancing force due to hydrostatic pressure than that provided by pumpslipper bearing 41. Since the injected speed-responsive or hydrodynamicbalancing pressure acts on about 20% less area in motor slipper bearing41' than in pump slipper bearing 41, the hydrodynamic balancing pressureprovides a smaller portion of total balancing pressure and lubricatingfluid flow. Since in motor 23' the hydrostatic pressure increases so asto overcome the load for low speed starting operation, the hydrostaticlubricating fluid supply must provide the hydrostatic balancing pressureand flow to meet the lubrication requirements of hybrid bearing 45' atthe hydrostatic load required at zero speed to start rotation or duringstarting operation. As speed increases, hydrodynamic balancing pressureand flow increase in order to meet increasing hydrodynamic load andspeed lubrication requirements. The increasing hydrodynamic balancingpressure and flow act to confine and reduce the hydrostatic balancingpressure and flow and to provide supplemental hydrodynamic balancingpressure to balance the remaining hydrostatic load at higher runningspeeds. The hydrostatic and hydrodynamic balancing pressures additivelycoact to provide higher total balancing pressure and flow varying withhydrostatic load and speed to meet the requirements of hybrid bearing45'. In motor 23', the hydrostatic balancing pressure provides a largerportion of total balancing pressure than that provided by thehydrodynamic balancing pressure to meet starting under load lubricationrequirements.

CONTROLS

The hydrostatic transmission 10, especially when used in the steer driveof a cross-drive transmission, has an input-driven input drive 91driving the pump 23 at or in a constant proportion to engine speed whichusually is governed. Hydrostatic transmission 10 is controlled byhydraulic controls 155 (FIGS. 11 and 12) to vary the displacement ofpump 23 and the speed of motor 23' so as to meet drive operationrequirements. In a steer drive, motor speed varies from zero forstraight drive to a maximum for the sharpest or smallest radius turn.Hydrostatic power pressure fluid is delivered by pump 23 to motor 23'.The hydrostatic power pressure varies with steer torque load from aminimum or supercharge pressure to a maximum pressure pressure value, asthe turning radius decreases to the tightest turn, pivot steer. Thehydrostatic power pressure in each of the pump cylinder chambers 42,during each revolution when pump 23 is driven, in the intake phase has asupercharge pressure value, and in the delivery phase has hydrostaticpower pressure at a value which varies from the supercharge pressurevalue at zero pump displacement and zero steer torque load for straightdrive, to a maximum pressure value at maximum steer torque load. Thehydrostatic power pressure in each of the motor cylinder chambers 42',during each revolution when hydrostatic pressure fluid is delivered bypump 23 to motor 23', in the intake phase is the hydrostatic pressurevalue and in the exhaust phase is the supercharge pressure. When pump 23is in a null (N) position having zero displacement (FIG. 2), thehydrostatic power pressure in pump and motor cylinder chambers 42 and42' is supercharge pressure, so there is no steer drive. In null (N)position pump 23 may have a small displacement, so the hydrostatic powerpressure value is slightly higher than supercharge pressure value tomore positively position the pump bearing ring 46. Hydrostatic powerpressure in each of the pump and motor cylinder chambers 42 and 42' actson the respective end area of each cylinder chamber to provide ahydrostatic load on pump and motor slipper bearings 41 and 41'proportional to hydrostatic pressure and steer torque load, and acentrifugal or hydrodynamic load proportional to speed.

The hydraulic steer controls 155 (FIG. 11) have a low pressure system160 with a low pressure supply 166 including regulated low pressuresource 156, e.g., an engine-driven pump and regulator valve, connectedto low mainline 157 to supply low mainline pressure, e.g., 150 psi (1034kPa). In low pressure system 160, low mainline 157 supplies charging andlubrication systems 326 and 328 and, in parallel, first pump 158 andsecond pump 159, both driven by a transmission element and connectedrespectively directly and through check valve 163 and forming a highpressure supply 167, to supply high mainline 161.

REGULATOR VALVES

High mainline 161 is connected to and regulated by primary regulatorvalve 164 (FIG. 11). High mainline 161 normally is connected withoutregulation, and at times connected with regulation, by secondaryregulator valve 165 to control pressure line 168.

Primary regulator valve 164 has a valve element 171 havingequal-diameter lands 171a and b slidable in a valve bore 172 in valvebody 169. In all positions of valve element 171, high mainline 161 isconnected to bore 172 between lands 171a and b, and connected by apassage 173 in valve element 171 extending through land 171a to a closedchamber 174 at the end of bore 172, so high mainline pressure acts onthe end area of land 171a in a pressure-decreasing direction to connecthigh mainline 161 to overage line 176 to decrease high mainline pressureby exhausting high mainline 161 and supplying overage line 176. Overageline 176, also a part of low pressure supply 166, is connected bycross-passage 306 of lubrication passage system 328 (described below),to low mainline 157 and always has low mainline pressure. Valve element171 is biased in a pressure-increasing direction by a spring 177, highsteer pressure actuator 178, and low mainline pressure. Spring 177 islocated in spring bore 179 which has a larger diameter than and iscoaxial with valve bore 172, and is seated on an end wall 181 secured tovalve body 169. Spring 177 acts through annular member 182 in engagementwith the end of land 171b to bias valve element 171 in apressure-increasing direction closing the connection of high mainline161 to overage line 176 for increasing high mainline pressure. Movementof valve element 171 in the pressure-increasing direction is limited byannular member 182 engaging stop 183 between bores 172 and 179.

Steer pressure actuator 178 has a small diameter actuator piston 184 inactuator bore 186 which has a smaller diameter than and is coaxial withvalve bore 172, in a cylinder 187. Cylinder 187 is formed as a portionof or attached to end wall 181 and located concentrically within spring177. Cylinder 187 also acts as a spring guide. The higher steer pressureline 188 is connected to actuator bore 186 to act on piston 184 whichextends through the center of annular member 182 to engage the end ofvalve element land 171b. An overage branchline 189, which may berestricted, connects overage line 176 to a closed chamber 191 in springbore 179, closed by end wall 181, so low mainline pressure acts on theend area of land 171b.

Overage line 176 is connected to low mainline 157 by lubrication passagesystem 328 (hereinafter described), and regulated low pressure source156 provides downstream regulation, so both overage pressure andlubrication pressure have the same constant low pressure value as lowmainline pressure. Overage, or low main pressure at the low mainlinepressure value, is supplied by overage branchline 189 to the closedchamber 191 in spring bore 179 and provides a constant bias force onvalve element 171 to reduce the bias force requirements of spring 177for more accurate calibration. The overage fluid pressure and springbias forces on valve element 171 provide a constant minimum high mainpressure (e.g., 400 psi [2758 kPa]), when the higher hydrostatic poweror steer pressure is in a low range, up to an intermediate pressurevalue (e.g., 200 psi [1379 kPa]). The high main pressure increases fromthe constant minimum pressure value in a reduced proportion to a maximumvalue (e.g., 400 to 1800 psi [1379 to 12,411 kPa]), as the higherhydrostatic steer pressure increases from the intermediate to a maximumvalue (e.g., 200 to 4000 psi [1379 to 27,580 kPa]).

The secondary regulator valve 165 has a valve element 196 havingequal-diameter lands 196a and b slidable in a valve bore 197 in thevalve body 169. The control pressure line 168 is connected to bore 197between lands 196a and b in all positions of valve element 196 and alsois connected via restricted branchline 198 to control pressure actuator199. Control pressure actuator 199 has a small diameter actuator piston201 slidable in a small diameter actuator bore 202 in end wall 203 ofvalve body 169. Control pressure from line 168 is supplied viarestricted branchline 198 to chamber 204 in the actuator bore 202 to acton actuator piston 201 which engages the end of land 196a to bias valveelement 196 to the exhaust or pressure-decreasing position shown (FIG.11), with a bias force proportional to control pressure. The low steerpressure actuator 206 has a large diameter actuator piston 207 slidablein large diameter actuator bore 208. Piston 207 has or engages aforce-strut 209 engaging the end of land 196b to bias valve element 196to the pressure-increasing position. A spring 211 is positioned inactuator bore 208, guided by force-strut 209, seated on a step 212between large actuator 208 and valve bore 197, and engages actuatorpiston 207 to bias piston 207 into contact with end wall 213 to permitcontrol pressure in control pressure actuator 199 to move valve element196 to the exhaust position. The low steer pressure line 214 has arestriction 216 and is connected, through end wall 213 to a chamber 217between end wall 213 and piston 207, to bias valve element 196 in acontrol pressure-increasing direction by a bias force proportional tolow steer pressure, as reduced by the bias force of spring 211. Withvalve element 196 in the exhaust position, secondary regulator valve 165connects control pressure line 168 to exhaust 218 and, in thepressure-increasing or connecting position, connects high mainline 161to control pressure line 168. Exhaust 219 vents valve bore 197 betweenland 196a and end wall 203. Exhaust 221 vents actuator bore 208 betweenvalve element 196 and piston 207.

As described below, low mainline 157 supplies lubrication fluid tolubrication passage system 328 and supercharge fluid to the lowerpressure one of charging passages 307, 307' of power transfer passagesystem 300; shuttle valve 311 supplies low steer pressure to the lowsteer pressure line 214. Low steer pressure, in a normal range betweenmainline pressure and an intermediate or signal pressure (e.g., 300 or150 psi to 80 psi [2068 or 1034 to 552 kPa]), indicates that thesesystems are supplied with normal operating pressure. Low steer pressureacts on low steer pressure actuator 206 to control secondary regulatorvalve 165 to regulate the control pressure in control pressure line 168.When low steer pressure is in the normal range, secondary regulatorvalve 165 is closed and control pressure is the same as high mainlinepressure. As low steer pressure decreases in an intermediate or signalrange, from the intermediate or signal pressure to a minimum operatingpressure (e.g., 80 to 30 psi [552 to 207 kPa]), secondary regulatorvalve 165 proportionally reduces the maximum available control pressure,from maximum high mainline and control pressure to zero (e.g., 1800 psi[12,411 kPa]), so as to reduce steer drive capacity to provide a signalwarning the operator of the decreasing charging and lubricationpressures, and to abort steer drive at minimum capacity operatingpressures.

STEER VALVE

The control pressure in control pressure line 168 (FIGS. 11 and 12) isselectively directed by steer valve 223 to the right and left steersignal lines 226 and 227 to control steer in accordance with steerdemand. The right and left steer signal lines 226 and 227 are connectedto the stroke limiter valve 216 to limit steer torque and to supplysteer control pressure, as described below, to right and left steercontrol lines 228 and 229. The right and left steer control lines 228and 229 are respectively connected to chambers or cylinders 74 and 76 ofright and left fluid motors 77 and 78 (described above), to control theposition of pump bearing ring 46 and the stroke or displacement of pump23 for steering. When there is no steer demand, the right and left steercontrol pressures supplied to right and left fluid motors 77 and 78 areequal, and position pump bearing ring 46 in the null or zero (N)displacement position (FIGS. 2 and 11) for neutral or straight-linedrive. When there is right or left steer demand, right or left steerpressure differential, sufficient to overcome the pump centering force,moves pump bearing ring 46 through increasing angular positions to themaximum right or left stroke (RS), (LS) positions for maximum right orleft steer.

The steer valve 223 comprises a cylindrical sleeve servo valve element231 rotatably mounted in a bore 232 in the valve body 233 fixed totransmission housing 11, and a steer valve element 246 rotatably mountedin the central bore 241 of servo valve element 231. A lever member 234has a ring portion 236 fixed on the end of servo valve element 231projecting from bore 232, and a lever portion 237 extending radiallyfrom the axis of rotation of servo valve element 231. Ring portion 236and a snap ring 238 secured on the opposite end of valve element 231engages the ends of valve body 233 to axially locate servo valve element231 in the bore 232. A link 239 is pivotally connected to lever portion237 and to pump bearing ring 46 to rotate servo valve element 231 fromnull or center (N) position to right or left steer (RS),(LS), positionsin proportion to pivotal movement of pump bearing ring 46 from null (N)position to right or left steer (RS),(LS), positions.

The servo valve element 231 has three annular channels a, b, and c, inits outer periphery, closed by bore 232 of valve body 233. Controlpressure line 168 is continuously connected to supply control pressure,via intermediate channel b and diametrically opposed inlet or controlpressure ports 242 in servo valve element 231 to feed supply recesses251 in steer valve element 246. Right steer signal line 226, whichcontrols right fluid motor 77, is continuously connected in servo valveelement 231 by channel a and diametrically opposed right control ports243--whose connection to supply and exhaust recesses 251 and 252 iscontrolled by steer valve element 246. Left steer signal line 227, whichcontrols left fluid motor 78, is continuously connected in servo valveelement 231 by channel c and diametrically opposed left control ports244--whose connection to supply and exhaust recesses 251 and 252 iscontrolled by steer valve element 246. These pairs of right and leftcontrol ports 243 and 244 are at right angles to each other; and thepair of control pressure ports 242 are located at half this angle, or45° from adjacent right and left control ports 243 and 244. The relativerotary positions of servo valve element 231 and steer valve element 246selectively control the connections between these pairs of ports.

A known manual steer lever or wheel may be connected by linkage (notshown) to rotate the steer lever 247 which is secured to steer valveelement 246 to rotate steer lever 247 and steer valve element 246 fromthe null or center (N) position shown in FIG. 12 for straight drive tosteer demand positions for right (RS) or left (LS) steer. An end wall249 is secured to or is a portion of steer valve element 246. End wall249 and steer lever 247 engage opposite ends of servo valve element 231to axially retain steer valve element 246 in the central bore 241 ofservo valve element 231.

As indicated above, steer valve element 246 has a pair of supplyrecesses 251 and a pair of exhaust recesses 252 formed therein, eachpair having diametrically opposed recesses in its periphery, closed bycentral bore 241. The pairs of recesses are at right angles to eachother. Exhaust recesses 252 are connected by diametrically opposedexhaust ports 253 to an exhaust passage 254, which extends axially insteer valve element 246 to the exhaust 255 through end wall 249. Theadjacent supply and exhaust recesses are separated by longitudinallyextending lands 256 which are slightly narrower than the diameters ofright and left control ports 243 and 244 in the servo valve element 231.Supply recesses 251 connect inlet ports 242 selectively to right andleft control ports 243 and 244; and exhaust recesses 252 selectivelyconnect right and left control ports 243 and 244, to exhaust fluidthrough exhaust ports 253 and exhaust passage 254 to exhaust 255.

The servo valve element 231 and manual steer valve element 246 are shown(FIG. 12) in their central or null (N) position in which manual steervalve 223 provides zero pump stroke. In null (N) position, lands 256 arealigned with right and left control ports 243 and 244. Manual steervalve 223 is an open-center type valve, since lands 256 are narrowerthan the diameters of ports 243 and 244, thus providing a clearancewhich permits controlled fluid flow between control pressure supplyrecesses 251 and right and left control ports 243 and 244 and betweenthese control ports and exhaust recesses 252. This causes the pressurein control ports 243 and 244 and in the respective cylinders 74 and 76of the stroke control fluid motors 77 and 78 to build to the same fluidpressure value (about half of low control pressure) to hold pump bearingring 46 at zero stroke, the null (N) position (FIGS. 2 and 11). Thehydrostatic pump 23, in null (N) position, does not deliver fluid todrive the hydrostatic motor 23'. Then when manual steer valve element246 is rotated in either direction, the control pressure supply recesses251 are further opened to one of the pairs of control ports 243 and 244,while the other pair of control ports is further opened to the controlexhaust recesses 252. For example, when the manual steer valve elementis rotated clockwise for right steer (RS), as viewed in FIG. 12, supplyrecesses 251 are further opened to right control ports 243, while leftcontrol ports 244 are further opened to exhaust recesses 252. Thiscauses a pressure imbalance or differential between cylinders 74 and 76,with the pressure increasing in right cylinder 74 and decreasing in leftcylinder 76. This causes piston 72 of right fluid motor 77 to movepiston 73 of left fluid motor 78, so both pistons move to change theangle of pump bearing ring 46 from null (N) position toward right steer(RS) position to increase the stroke of hydrostatic pump 23. Thus,hydrostatic pump 23 is caused to deliver high hydrostatic power pressurefluid to drive hydrostatic motor 23' in the direction for right steer(RS), the fluid delivery in this condition being from pump 23 to rightpower transfer passage 301. Since pump bearing ring 46 is connected bylink 239 to lever portion 237 of servo valve element 231, servo valveelement 231 rotates to follow manual steer valve element 246. When servovalve element 231 nearly catches up with the steer valve element 246,their relative normal constant steer positions are reestablished withthe pressure in both right and left cylinders 74 and 76 having aconstant steer, low pressure differential which is sufficient toestablish equilibrium. Thus, with the displacement of control motor 77having increased and the displacement of control motor 78 havingdecreased and with equilibrium established, the pump bearing ring willremain in a constant steer position. The constant steer differentialpressure in cylinders 74 and 76 balances the pump bearing ring 46reaction forces to hold pump bearing ring 46 in the advanced right steer(RS) position corresponding to the advanced right steer (RS) position ofmanual steer valve element 246 until steer valve element 246 is moved.With the structural symmetry provided, manual steer valve element 246and servo valve element 231 cooperate, when steer valve element 246 isrotated in the opposite direction, to decrease the right steer angle ofpump bearing ring 46 to null (N) position and on further movement toleft steer (LS) position, to provide further movement in the oppositedirection to a left steer (LS) angular position of pump bearing ring 46to reverse the direction of fluid flow to the hydrostatic motor 23'(i.e., high hydrostatic power pressure fluid flows to left powertransfer passage 301'), so that motor 23' is driven in the oppositedirection.

STROKE LIMITER VALVE

A stroke limiter valve 261 (FIG. 11) under conditions which would causea torque overload on the hydrostatic pump 23, interrupts, limits, orreverses the pressure of the control fluid selectively supplied by steervalve 223 to the right or left steer signal lines 226 or 227 duringtransfer to right or left steer control lines 228 or 229, so that thedegree of steer demanded by the vehicle operator is overridden to theextent of limiting steer and thus torque requirements to the degreepossible without pump and steer system torque overload. The strokelimiter valve 261 comprises a valve element 262 having equal-diameterlands a, b, c, d, and e, located in a bore 263 of a sleeve 264 which isfixed in valve body 266. On each side of central land 262c, there isrespectively an intermediate land b and d and an end land a and e. Thespace between intermediate and end lands b and a is connected by apassage 267, through land a to the end of valve element 262. Similarly,the space between intermediate and end lands d and e is connected by apassage 268, through land e to the end of valve element 262. Right andleft biasing assemblies 271 and 271', respectively responsive to rightand left steer pressure, are similar and are located at opposite ends ofstroke limiter valve 261 to normally bias valve element 262 to thecentral position shown in FIG. 11. Right biasing assembly 271 has a cupmember 272 which is secured in a large bore 273 in valve body 266 bythreads 274 and has a lip clamping an annular abutment 276 against ashoulder at the end of large bore 273 and valve sleeve 264. In chamber277 in cup member 272 there is a biasing spring 278 which, at its outerend, contacts the base of cup member 272 and at its inner end, contactsthe shoulder 279 of a piston 281 to urge piston 281 toward the valvecenter against the annular abutment 276. Located within spring 278 is acylinder 282 having a closed-end bore 283 in which the piston 281 islocated. A damper spring 284 is located in the damping chamber 286between the closed end of cylinder bore 283 and piston 281. Dampingchamber 286 is connected to the surrounding chamber 277 by a restrictedpassage 287 in cylinder 282. Cylinder 282 is bottomed or engages at itsouter end on the base of cup member 272. Biasing spring 278 provides themajor bias force and damper spring 284 provides a minor bias force forbiasing piston 281 so its shoulder 279 normally engages the annularabutment 276 and biases valve element 262 to the central position shown.A passage 288 in piston 281 connects the end of piston 281 adjacent theland e end of valve element 262 to chamber 277 of cup member 272.

Stroker limiter valve 261 has a similar left biasing assembly 271' atthe opposite end, so the same reference numerals (primed) have beenused, and reference is made to the above description of right biasingassembly 271. Right and left annular abutments 276 and 276' secure valvesleeve 264 in the valve body 266. Right and left biasing springs 278 and278', with a little assistance from right and left damper springs 284and 284', bias valve element 262 to the central position shown in FIG.11.

The right and left steer signal lines 226 and 227 are respectivelyconnected to right and left signal ports 291 and 292 centrally locatedin valve sleeve 264; right and left steer control lines 228 and 229 arerespectively connected to right and left feed ports 293 and 294 andright and left control ports 296 and 297 in valve sleeve 264. The rightand left control ports 296 and 297 are near opposite ends of valvesleeve 264 and respectively adjacent right and left feed ports 293 and294 which, in turn, are respectively adjacent right and left centrallylocated signal ports 291 and 292. The right and left load signal lines298 and 299 are respectively connected to right and left chambers 277and 277' of cup member 272, and right and left passages 288 and 288' inpiston 281, to act on opposite ends of valve element 262 and forconnection to right and left passages 268 and 267 which are blocked,with valve element 262 in the central position.

During right steer, right load signal line 298 has the high hydrostaticpower pressure and left load signal line 299 has charging pressure,providing a hydrostatic differential pressure proportional to steertorque load which biases valve element 262 to right steer torquelimiting positions. During left steer, the pressures in these loadsignal lines and the hydrostatic differential pressure are reversed.

During steering operation in the normal or permitted torque load range,the centering bias force of biasing springs 278 and 278' and dampersprings 284 and 284' is sufficient to overcome either right or leftsteer hydrostatic differential pressure bias force to retain valveelement 262 in the central stroke permit position shown. In the pumpstroke permit position, valve element 262 connects right steer signalline 226--through right signal port 291 between lands 262b and c, andthrough right feed port 293 in sleeve 264, to right steer control line228 leading from stroke limiter valve 261 to right fluid motor 77, forpump stroke control. The left steer signal line 227 is connected by leftsteer signal port 292, between lands 262c and d, to left feed port 294and left steer control line 229 supplying left fluid motor 78. The rightand left control ports 296 and 297 are respectively blocked by end lands262a and e. On movement of valve element 262 in either direction bycertain hydrostatic differential pressure values (hereinafterdescribed), the stroke limiter valve 261 controls the pressure in rightand left steer control lines 228 and 229 to limit pivotal movement ofpump bearing ring 46 from null (N) position and thus limit hydrostaticpump stroke to limit steer torque.

The right pump kidney port 302 of hydrostatic pump 23, having highpressure during right steer, is connected via right load signal line 298to cup member right chamber 277 of stroke limiter valve 261. The leftpump kidney port 302' of the pump 23, having high pressure during leftsteer, is connected via left load signal line 299 to the left chamber277'. With right and left chambers 277 and 277' connected through rightand left piston passages 288 and 288' to the opposite ends of sleevebore 263, the hydrostatic differential pressure across the hydrostaticpump 23 is applied to act on the equal end areas of valve element 262 atlands 262e and a. This pressure differential is zero when thehydroxtatic pump 23 is at zero stroke, with the hydrostatic system 300including right and left power transfer passages 301 and 301' suppliedwith fluid at the charging pressure, hereinafter described in greaterdetail.

Under normal steer conditions which would not overload the hydrostaticpump 23, the hydrostatic differential pressure of pump 23 acting onvalve element 262 is insufficient to overcome the bias force of theopposing one of biasing springs 278, 278', plus the small bias force ofthe opposing one of damper springs 284, 284', so that the valve element262 is held in its stroke permit position shown (FIG. 11) to maintainconnection of right and left steer signal lines 226 and 227 to delivercontrol pressure respectively to right and left steer control lines 228and 229 so as to control pump stroke, and the degree of steer inaccordance with steer demand. Under conditions which would overload thesteer system, especially hydrostatic pump 23, the higher hydrostaticdifferential pressure is effective to move the valve element 262 toright or left stroke limiting positions. For example, when the steervalve 223 is controlled by the vehicle operator for right steer toeffect right steer movement of right and left stroke control fluidmotors 77 and 78 and pump bearing ring 46 toward or to right steerposition (RS), which results in fluid flow by hydrostatic pump 23 fromleft power transfer passage 301' at charging pressure to right powertransfer passage 301 at a higher hydrostatic power pressure, and anincrease of steer load occurs, the right hydrostatic power pressureincreases, thus increasing the hydrostatic differential pressure. Atmaximum torque load, maximum hydrostatic differential pressure overloadsignal signals that the pump is at the limit of its load capacity. Thismaximum hydrostatic differential or overload pressure signal istransmitted by right and left load signal lines 298 and 299 to thechambers 277 and 277' to act across the valve element 262. This overloadsignal urges valve element 262 leftwardly (FIG. 11) to right steercontrol positions to control the pressure supplied by right steercontrol line 228 to right fluid motor 77. Under these conditions, rightsteer signal line 226 and right steer control line 228 normally would bemaking increasing high control pressure available to right steer controlfluid motor 77 for movement or holding by this motor 77 to effect highpump displacement for the steer being demanded. But with the strokelimiter valve element 262 in a first right steer limiting phase, land262c progressively closes right signal port 291 to reduce fluid flowfrom right steer signal line 226, and land 262a progressively opensright control port 296 for exhaust fluid flow from right steer controlline 228 through right control port 296 and passage 267 to left chamber277' which is at charging or low main pressure to progressively decreaseright steer control pressure in line 228 to low main pressure when rightsignal port 291 is closed and right control port 296 is open. If thisreduction of right steer control pressure in right steer control line228 does not reduce right power pressure in right power transfer passage301 and right load signal line 298 below the overload limit value, thecontinued overload signal will further move valve element 262 to asecond right steer limiting phase. In this second right steer limitingphase, the high hydrostatic power pressure in right load signal line 298is delivered via chamber 277 and passage 288 in piston 281 of rightbiasing assembly 271 and then via passage 268 in valve element 262 andnow connected by left feed port 294 to left steer control line 229 andleft cylinder 76. With the high right power pressure replacing low mainpressure in left cylinder 76 and low main pressure replacing highcontrol pressure in right cylinder 74, left fluid motor 78 will providea force in addition to the inherent centering force, proportional topump torque of pump 23 to return pump bearing ring 46 from right steer(RS) position toward null (N) position to reduce right power pressure inright power transfer passage 301 below the overload limit value.

When pump bearing ring 46 is moved in the opposite direction toward leftsteer (LS) position by left steer control pressure in left fluid motor78 under the control of steer valve 223 resulting in fluid flow byhydrostatic pump 23 from right power transfer passage 301 to left powertransfer passage 301' and the steer load increases to the overload limitof hydrostatic pump 23, the hydrostatic differential pressure of pump 23is transmitted to the stroke limiter valve 261 to move valve element 262to left steer (LS) limiting positions, to the right in FIG. 11.

The stroke limiter valve 261 is symmetrical about its center and, inresponse to similar but opposite left limiting movement, functions in amanner similar to that described above for right steer: to first reduceleft steer control pressure in left steer control line 229 to low mainpressure and then replace low main pressure in right steer control line228 with the high left hydrostatic power pressure from left powertransfer passage 301', to move pump bearing ring 46 from left steer (LS)position toward null (N) position to reduce left hydrostatic powerpressure to the overload limit value. The stroke limiter valve 261limits the stroke of hydrostatic pump 23 in response to overload tolimit steer to less than the steer demanded by the operator to avoidoverloading the hydrostatic system. When the differential pressureacross the hydrostatic pump 23 decreases to below the overload limitvalue, the stroke limiter valve element 262 is spring-biased to thestroke permit position shown in FIG. 11 for normal steer control.

HYDROSTATIC POWER TRANSFER

Referring to FIGS. 1, 2, and 10, with pump bearing ring 46 in the null(N) position shown in FIGS. 2 and 10, the pump 23 does not deliverhydrostatic power pressure for neutral operation, so the entire powertransfer passage system 300 is at charging pressure and no power istransferred for steering to provide straight drive. When pump bearingring 46 is moved to the right steer (RS) position--with pump 23 drivenin the direction of pump rotation (Arrow PR, FIG. 2), pump 23 delivershigh hydrostatic power pressure through right power transfer passage 301to motor 23' to drive the motor 23' in the same direction of rotation(Arrow MRRS) for right steer drive. In the left steer (LS) position,pump 23 delivers high hydrostatic power pressure through left powertransfer passage 301' to drive motor 23' for motor rotation in theopposite direction (Arrow MRLS) for left steer drive. During right steeroperation of pump 23 with pump bearing ring 46 in right steer (RS)position, pump piston and cylinder members 29 and 39 deliver highhydrostatic power pressure via pump rotor ports 32 to right pump kidneyport 302 (acting as a delivery port), through right power transfer 301(formed by four right axial bores 303), to right motor kidney port 304(acting as an inlet port), to motor rotor ports 32', to motor piston andcylinder members 29' and 39', to drive motor 23' in the direction (ArrowMRRS) for right steer drive.

The left power transfer passage 301' is similar to right power transferpassage 301 described above but is located on the opposite side inpintle 19, as shown in FIGS. 2 and 11, with like numerals (primed).

During right steer operation, motor 23' exhausts hydrostatic fluid atcharging pressure via a left kidney port (not shown) acting as anexhaust port to left power transfer passage 301' to left pump kidneyport 302' acting as the inlet port. During left steer operation of pump23, with pump bearing ring 46 in the left steer (LS) position, thehydrostatic power fluid flow is reversed and similarly left powertransfer passage 301' delivers high hydrostatic power pressure to drivemotor 23' in the opposite direction (Arrow MRLS) for left steer, andright power transfer passage 301 returns power fluid at chargingpressure from motor 23' to pump 23.

In low pressure system 160 low pressure supply 166 (FIG. 11) has lowmainline 157 and cross-passage 306 for connection to operation supportsystem 325 having charging and lubrication systems 326, 328. Chargingsystem 326 has right and left charging passages 305,305', respectivelyhaving right and left check valves 308,308', to supply charging fluid atlow mainline pressure to the one or both of the right and left charginginlet passages 307, 307', and ports 309 and 309' of power transfersystem 300 having hydrostatic charging pressure.

Check valves 308 and 308' prevent return of higher hydrostatic powerpressure fluid to low mainline 157. As shown in FIG. 2, right chargingport 309 in pintle 19 is formed by cross-bores to connect right chargingpassage 307 in support wall 16 to all four axial bores 303 which formright power transfer passage 301. The left charging port 309' is formedas one bore to connect left charging passage 307' to all four axialbores 303' which form left power transfer passage 301'. Plugs 310 and310' close the ends of charging passages 305 and 305', beyondcross-passage 306 at the edge of central support wall 16. Right and leftpower transfer passages 301 and 301' are respectively connected viaright and left charging passages 307 and 307' to right and left powerpressure or load signal lines 298 and 299 to supply right and left powerpressures which increase above charging pressure respectively inproportion to right and left steer load.

SHUTTLE VALVE

Shuttle valve 311 has a valve element 312 having equal-diameter lands a,b, and c, slidable in a bore 313 between right and left positionslimited by respective right and left end walls 316 and 317. Valveelement 312 has a passage 318 formed therein connecting the spacebetween lands 312a and b through land a to the end of valve element 312to supply the chamber 319 located at the left end of bore 313. Valveelement 312 has a similar passage 321 connecting the space between lands312b and c through land c to supply the chamber 322 at the opposite orright end of bore 313. In all positions of valve element 312 right loadsignal line 298 is connected to the space between lands 312b and c viapassage 321 to right end chamber 322. Left load signal line 299 isconnected to the space between lands 312a and b via passage 318 to leftend chamber 319. During left steer operation, the higher hydrostaticpower pressure in left load signal line 299 and in chamber 319 movesvalve element 312 against low mainline or charging pressure in chamber322 to the left steer position shown (FIG. 11), supplying higher leftsteer hydrostatic pressure as a load signal pressure between lands 312aand b to higher steer pressure line 188, and charging hydrostaticpressure or low steer pressure in right load signal line 298 isconnected between lands 312b and c via branch 323 to low steer pressureline 214. Conversely, during right steer operation, the higher rightsteer pressure in chamber 322 and charging pressure in left end chamber319 moves valve element 312 to the opposite right steer positionconnecting the higher hydrostatic power pressure in right load signalline 298 between lands 312b and c to higher steer pressure line 188, andconnecting lower hydrostatic power pressure left load signal line 299via branch 324 to low steer pressure line 214.

LUBRICATION SUPPLY

As shown schematically in FIG. 11 and more structurally in FIGS. 2 and3, low mainline 157 is connected by cross-passage 306 to charging system326, lubrication system 328, and overage line 176 by connection 327.Regulated low pressure source 156 provides a supply and downstreampressure regulation for the interconnected low mainline 157, overageline 176, and lubrication passage system 328. Thus lubrication systempressure, charging pressure, and overage line pressure are the same aslow mainline pressure, and overage fluid is supplied to the lubricationand charging systems 328 and 326 to minimize regulated low pressuresource requirements and excess fluid may be returned and exhausted atsource 156. Cross-passage 306 is a low pressure fluid connecting part oflow pressure system 160 and its subsystems, low pressure supply 166, inwhich it connects low main and overage lines 157, 176, and operationsupport system 325 having subsystems, charging system 326, in which itconnects to charging passages 305, 305', and lubrication system 328.Overage line 176 supplies fluid under the same pressure via connection327 at support wall 16 to inlet passage 329 and annular passage 331around pin 58 for lubrication of pin 58 in bearing bore 59 andconnection to cross-passage 306. First and second transverse passages332 and 333 in support wall 16 intersect and extend transverselyrelative to cross-passage 306. Plugs 334 and 335 (FIG. 2) seal thesepassages at the outer edge of central support wall 16. First transversepassage 332 extends in central support wall 16 to the circular opening17 for supporting pintle 19 for connection (FIGS. 1 and 2) throughradial passage 337 in pintle 19 to supply fluid for lubrication to theconnected axial passage 338 which is closed at both ends of pintle 19.First transverse passage 332 (FIGS. 2 and 3) has a pump jet opening 341and a motor jet opening 341'. Pump jet opening 341 has a nozzle 342located at first transverse passage 332 near the radial inner portion ofcentral support wall 16 and is laterally angled so as to direct a jetstream 343 of fluid for lubricating at a lateral angle (e.g., 45°)through passage 344 and to impinge on pump piston and cylinder members29 and 39 for their lubrication and cooling, and between pump piston andcylinder members 29 and 39 to impinge on pump internal bearing surface44 of pump bearing ring 46 at the center, on pump centerline (PC) ofinternal bearing surface 44 in null (N) position. Motor jet opening 341'similarly has a nozzle 342' similarly located and oppositely laterallyangled to direct a jet stream 343' to impinge on motor internal bearingsurface 44' of motor bearing ring 46' at the motor centerline.

The second transverse passage 333 has similar pump and motor jetopenings 346 and 346' directing jet streams of fluid for lubricatingradially outwardly and laterally respectively to the centers of pump andmotor internal bearing ring surfaces 44 and 44'. The jet streams impingeon the pump and motor piston and cylinder members 29,29' and 39,39' forlubrication and cooling, and on the pump and motor internal bearing ringsurfaces 44 and 44', in their upper quadrants, between the cylindermembers 39 and 39', and fluid is retained thereon by annular dams 47 and47'. Rotation of cylinder members propels or moves oil beyond or aheadof the cylinder members 39 and 39' as the members rotate around theentire perimeters of the respective pump and motor internal bearing ringsurfaces 44 and 44' for the above-described hydrodynamic lubricationcomponents 139 and 139' of hybrid bearings 45 and 45'.

Lubricating fluid supplied to axial passage 338 is also connected bypump and motor restricted radial feed passages 347 and 347' to lubricatethe pump and motor rotor internal bearings 27 and 27' on pump and motorbearings 28 and 28' on pintle 19. Pump rotor internal bearing 27 has, atopposite side edges, internal annular grooves 348 and 349 to collecthydrostatic leakage fluid and to distribute this leakage fluid forlubrication. Pump radial feed passage 347 is connected to and suppliesfluid to annular groove 348. Annular grooves 348 and 349 are connectedby passages 351 and 352 to a nozzle 353 formed integrally in or attachedto pump rotor 24 centrally between each of the piston members 29 toprovide a jet stream of fluid impinging on internal bearing ring surface44 between each of the cylinder members 39 for a supplemental oralternative feed of the pump hydrodynamic bearing component 139employing hydrostatic leakage fluid and lubrication supply fluid. Themotor rotor internal bearing 27' has similar annular grooves 348' and349' connected by passages to a nozzle (not shown) to similarly providea lubrication fluid jet stream impinging on motor internal bearing ringsurface 44'.

OPERATION

When the engine is running and driving the transmission input drive 91,the regulated low pressure source 156, which includes a pump anddownstream regulator, is driven to supply low mainline pressureregulated at a low pressure (e.g., 150 psi) to low mainline 157, and atleast one of first and second pumps 158 or 159 is driven to supply highmainline pressure to high mainline 161. The primary regulator valve 164regulates high mainline pressure in high mainline 161 in a high pressurerange (e.g., 400 to 1800 psi) proportional to high hydrostatic powerpressure, and connects the overage fluid flow to overage line 176. Sinceoverage line 176 is connected to the lubrication passage system 328 andto low mainline 157, these lines have regulated low mainline pressure.Low mainline 157 and at times overage line 176 supply lubricationpassage system 328 and, through check valves 308 and 308', charge powertransfer passage system 300, so hydrostatic transmission 10 is operativefor null and steer drive operation. When low mainline pressure forcharging and lubrication is normal, the secondary regulator valve 165connects high mainline 161 to control pressure line 168 to supply manualsteer valve 223 so hydraulic steer controls 155 are operative.

When there is no steer demand steer valve 223 is in null (N) position,so hydraulic steer controls 155 position pump bearing ring 46 in null(N) position for straight drive operation. In the power transfer passagesystem 300, since pump 23 is not pumping, the right and left powertransfer passages 301 and 301' respectively have right and lefthydrostatic power pressure equal to the charging pressure, which is lowmainline pressure. During right and left steer drive operation therespective one of the right and left hydrostatic power pressuresincreases from low mainline charging pressure to a maximum (e.g., 150 to4000 psi) with increasing steer torque load, while the other pressureremains at or below low mainline or charging pressure. The shuttle valve311 supplies the higher hydrostatic power pressure to higher steerpressure line 188 and the low hydrostatic charging pressure to low steerpressure line 214.

In response to steer demand by movement of steer lever 247 toward or toright or left steer (RS) or (LS) demand position, on opposite sides ofnull (N) position, steer valve 223 controls the supply of controlpressure from control pressure line 168 respectively to right and leftsteer signal lines 226 and 227 which, in the normal steer torque loadrange, are freely connected by stroke limiter valve 261 to right andleft steer control lines 228 and 229 supplying right and left fluidmotors 77 and 78 to position pump bearing ring 46 in right and leftsteer drive (RS) and (LS) positions on opposite sides of null (N)position corresponding to the steer demand position of steer lever 247.

The primary regulator valve 164 has a constant bias force provided byoverage and low mainline pressures which is equal to that of regulatedlow mainline pressure valve and by spring 177 to regulate a minimum highmainline pressure (e.g., 400 psi), as the high hydrostatic powerpressure in high steer pressure line 188 increases in a low range up toa low value (e.g., 200 psi), and to regulate high mainline pressureincreasing from the minimum to a maximum pressure (e.g., 400 to 1800psi), in proportion to the increase of high hydrostatic power pressurefrom the low to a maximum pressure value (e.g., 150 to 4000 psi). Thushigh mainline pressure provides a control pressure acting in fluidmotors 77 and 78 to control pump stroke meeting, but not significantlyexceeding, stroke control force requirements which increase with pumptorque load and high hydrostatic power pressure to minimize parasiticpower loss.

The secondary regulator valve 165 is controlled by the low charginghydrostatic power pressure in low steer pressure line 214 acting on lowsteer pressure actuator 206. Secondary regulator valve 165 normallyconnects high mainline pressure in high mainline 161 to control pressureline 168 when the lower hydrostatic power pressure in the right or leftpower transfer passages 301 and 301' is above the normal operatingminimum pressure value (e.g., 80 psi) for normal operation of thecharging system and hydrostatic and hydrodynamic lubrication systems ofpump 23 and motor 23'. In the normal operating range of low hydrostaticpower pressure values from the regulated low mainline pressure value(e.g., 150 psi), to the normal operating minimum pressure value (e.g.,80 psi), permits normal transient pressure variation, due to normal highflow requirements variation relative to supply capacity, with sufficientlow mainline pressure and fluid flow for proper charging andlubrication, and sufficient high mainline pressure for proper strokecontrol up to maximum high hydrostatic pressure and load limited bystroke limiter valve 261.

Abnormal conditions (e.g., severe load, high temperature, or damage) inhydrostatic transmission 10 may cause leakage at a rate abnormallyhigher than the supply rate capacity of low pressure source 156 andoverage resulting in a further reduction of low hydrostatic pressure inan abnormal operating range. When the lower pressure of the right andleft hydrostatic pressures in power transfer passages 301 and 301'decreases in the abnormal operating range from the normal operatingminimum pressure value to a minimum operating pressure value, steercontrol pressure and thus pump torque load capacity is proportionatelyreduced to zero. The lower or charging hydrostatic power pressure isconnected from one of power transfer passages 301 or 301' and connectedright or left load signal lines 298 or 299 having the lower hydrostaticpower pressure by shuttle valve 311 to low steer pressure line 214 tocontrol the secondary regulator valve 165 to proportionately reduce orlimit control pressure in control pressure line 168 from the highmainline pressure value regulated by the primary regulator valve 164 tozero as lower or charging hydrostatic power pressure decreases from thenormal operating minimum pressure value to a minimum operating pressurevalue (e.g., 80 to 30 psi). This reduction of control pressure in theabnormal operating range induces the capacity of the steer controls tocontrol pump stroke to provide high values of high hydrostatic powerpressure, so the high hydrostatic power pressure and load is limited orreduced. This reduction or limitation of high hydrostatic power pressurewill reduce the degree of steer response relative to the degree of steerdemand or degree of steer operation and advise the operator that lowhydrostatic power pressure, charging pressure, and lubrication pressureare low (in the abnormal range), and that steer demand has beenexcessive or service is required. This reduction of control pressurereduces high hydrostatic power pressure and load capacity so that thereduced charging and lubrication pressures are sufficient for properoperation, especially at this reduced load. If excess steer demand andresultant high temperature caused the abnormal low hydrostatic powerpressure, operation at reduced load will reduce leakage and temperature,so low hydrostatic power pressure will increase to the normal range.This control pressure reduction, when due to a service-related problem,is normally gradual and permits limited load and degree steeringoperation for a considerable time for vehicle retrieval. When low powerpassage pressure is below the minimum pressure value (e.g., 30 psi),there are insufficient charging and lubrication pressures for properoperation of hydrostatic transmission 10, so the control pressure isreduced to zero to abort operation of or unload hydrostatic transmission10.

For straight drive, steer valve 223, in straight drive or null (N)position, positions pump bearing ring 46 in null (N) position sohydrostatic transmission 10 is in neutral, with the variabledisplacement pump 23 in zero stroke position. In the straight drive ornull (N) position of steer valve 223, steer valve element 246 ismanually positioned in null (N) position, and servo valve element 231 ispositioned in null (N) position by link 239 connected to pump bearingring 46 in null (N) position to connect control pressure line 168 toboth the right and left steer signal lines 226 and 227. Since steervalve 223 is an open-center valve connecting, through a clearance, theright and left steer signal lines 226 and 227 to control pressure line168 and exhaust 255, the right and left steer signal pressure values areequal and about one-half of the control pressure value. Thus, with equalpressure in right and left fluid motors 77 and 78 and the inherentself-centering forces of pump 23 on pump bearing ring 46, the pumpbearing ring is held in the null (N) position for zero stroke. Right andleft power transfer passages 301 and 301', charging passages 307 and307', connected load signal lines 298 and 299, high and low steerpressure lines 188 and 214, and the lubrication passage system 328, allare supplied by low mainline 157 and overage line 176 and thus have lowmainline pressure, e.g., 150 psi. Control pressure in control pressureline 168 will be regulated by primary regulator valve 164 at minimumpressure value, e.g., 400 psi.

When the vehicle operator moves manual steer lever 247 from the null (N)position to any right steer demand position, including full right steerdemand (RS) position, steer valve element 246 is similarly rotated toconnect control pressure line 168 to supply full control pressure toright steer signal line 226 and to exhaust left steer signal line 227,connected via stroke limiter valve 261 and respectively right and leftsteer control lines 228 and 229 to cylinders 74 and 76 of right and leftfluid motors 77 and 78, to move pump bearing ring 46 from null (N)position toward or to maximum right steer (RS) position to increaseright steer stroke of pump 23. Then pump 23 pumps fluid to increasehydrostatic power pressure in right power transfer passage 301 to drivemotor 23' to meet right steer requirements. This higher hydrostaticpower pressure, connected via right load signal line 298, shuttle valve311, and high steer pressure line 188, controls primary regulator valve164 to increase high mainline and control pressures to meet pump strokecontrol requirements. Pump bearing ring 46 is connected by the link 239and steer lever 247 to rotate servo valve element 231 to the same degreeas manual steer valve element 246 in response to the degree of strokechange demanded. When pump bearing ring 46 reaches the demanded strokeposition, up to the maximum stroke (RS) position, servo valve element231 catches up with manual steer valve element 246 to provide asteer-hold position which, like null (N) position, provides controlpressure to both right and left steer signal lines 226 and 227 and thefluid motors 77 and 78 having a sufficient pressure differential tobalance the pump load reaction on pump bearing ring 46 to hold pumpbearing ring 46 in the demanded stroke position.

For left steer drive, the steer lever 247 is moved from null (N)position toward or to full left steer (LS) position--depending on thedegree of steer demand, and these controls similarly provide thedemanded degree of left steer drive.

As pointed out above, if the demanded degree of steer drive results in atorque overload on pump 23, the stroke limiter valve 261 controls theright and left steer control pressures delivered to right and left steercontrol lines 228 and 229 to limit pump stroke and thus steer torque tothe rated torque capacity of pump 23 and hydrostatic transmission 10.

In the operation of hydrostatic transmission 10, pump 23 first rotatesat low starting speeds while it is unloaded and has about charginghydrostatic power pressure. Then as pump speed increases to higherrunning speeds, the higher hydrostatic power pressure increases tohigher pressure values with the drive torque load. During coast, thehigher hydrostatic power pressure may be reduced to the chargingpressure. Overrun drive will reverse the charging and higher hydrostaticpower pressures in right and left power transfer passages 301 and 301'of the power transfer passage system 300.

The operating relation of the main and component systems or means aresummarized below. In the hydraulic steer controls 155, the low pressuresystem includes a low pressure supply 166 and the operation supportsystem 325.

The low pressure supply 166 has a regulated low pressure source 156supplying regulated low pressure via low mainline 157, and overage line176 supplying fluid flow at regulated flow pressure from primaryregulator valve 164 via overage line 176 and cross-passage 306. The lowpressure supply 166 also supplies the operation support system 325 andhigh pressure supply 167. The operation support system 325 includes thecharging system 326 supplied from cross-passage 306 and having right andleft charging passages 305 and 305' and respective check valves 308 and308' for charging the hydrostatic power transfer system 300; and thelubrication system 328 having cross-passage 306 for supply, and firstand second transverse passages 332 and 333, and radial and axialpassages 337 and 338 to distribute the lubricating fluid. The lowpressure system 160 also supplies the high pressure supply 167 havingpumps 158 and 159 for supplying primary and secondary regulator valves164 and 165, steer control valve 223, stroke limiter valve 261, shuttlevalve 311, and fluid motors 77 and 78 of hydraulic steer controls 155for stroke control of pump 23.

MODIFICATION

The modified secondary regulator valve 165' of FIG. 13 is similar to theabove-described secondary regulator 165 of FIG. 11, so like referencenumerals (primed) have been used, and reference is made to the abovedescription for like features, and to the following description of themodifications.

In the modified secondary regulator valve 165', the valve element 196',bore 197', control pressure actuator 199', low steer pressure actuator206', the exhausts 219' and 221' for venting valve bore 197' andactuator bore 208', are the same as these counterparts in the preferredsecondary regulator valve 165. In modified secondary regulator valve165', high mainline 161' is connected directly to control pressure line168' which is similarly connected by restricted branch 198' to controlpressure actuator 199' and to manual steer valve 223 (FIG. 11), and alsodirectly connected to valve bore 197' at a point always between lands a'and b' of valve element 196'. The control pressure actuator 199' and lowsteer pressure actuator 206' similarly bias valve element 196' forpressure regulation of control pressure in high mainline 161' andcontrol pressure 168' by exhausting control pressure fluid to exhaustport 218' which is connected to low steer pressure line 214' to supplythis exhaust or overage fluid flow, via shuttle valve 311 (FIG. 11), tothe one of the right and left pump kidney ports 302 or 302' having lowor charging pressure. Since the modified secondary regulator valve 165'regulates reduced control pressure by blocking or connecting exhaustflow from high mainline 161' to exhaust port 218', this valve 165' musthave a large diameter so the exhaust flow capacity is larger than thesupply flow capacity of first and second pumps 158 and 159 (FIG. 11)supplying high mainline 161'. Since the preferred secondary regulatorvalve 165 regulates by blocking or connecting flow from high mainline161 alternatively to control pressure line 168 and exhaust 218, a smalldiameter, low flow capacity regulator valve is sufficient forregulation.

Modified secondary regulator valve 165' blocks exhaust port 218' whenlow steer or hydrostatic pressure is in the normal range, so highcontrol pressure is the same as high mainline pressure, proportional tohigh steer or hydrostatic pressure. As low steer pressure decreases inan abnormal range to a minimum operating pressure value, the controlpressure is proportionally reduced to zero to discontinue or abort steerdrive. The low steer or charging hydrostatic pressure normally is thesame as low supply pressure in low mainline 157. The regulated highcontrol pressure values regulated in response to low steer pressure inthe normal and abnormal ranges by the modified secondary regulator valve165' are similar to those described above for the preferred secondaryregulator valve 165.

During operation in the normal pressure range of low hydrostatic powerpressure, in both embodiments secondary regulator valves 165 and 165'are closed, and primary regulator valve 164 regulates high mainline andcontrol pressures and connects all overage fluid flow to the lowpressure system 160. During operation in the abnormal lower pressurerange of low hydrostatic power pressure, the regulation by modifiedsecondary regulator valve 165' supplies all overage fluid flow in lowsteer pressure line 214' to the right or left hydrostatic power transferpassage 301, 301', having low or charging pressure. Then primaryregulator valve 164 is closed and does not provide overage fluid flow.The reduced pressure in overage line 176 of the low pressure system 160is equal to low hydrostatic pressure and has no effect on the closedprimary regulator valve 164. During operation in the abnormal pressurerange, the preferred secondary regulator valve 165 provides only a smallamount of flow from high mainline 161 selectively to control pressureline 168 and a small amount of flow to exhaust 218 to meet pump 23displacement control flow requirements at high control pressure, sosubstantially all overage fluid flow is connected by primary regulatorvalve 164 to the low pressure system 160.

It will be appreciated that further modifications of the invention maybe made.

The embodiments of the invention for which an exclusive property orprivilege is claimed are defined in the following claims:
 1. In ahydrostatic transmission: hydrostatic power transfer means including anormally driven pump, a normally driving motor, two passages connectingsaid pump and motor for torque transfer therebetween with one passagehaving high hydrostatic pressure and the other passage having lowhydrostatic pressure, fluid operated displacement varying meansoperative in response to control pressure for varying the relativedisplacement of said pump and motor to vary the torque ratio and havingthe capacity to provide said high hydrostatic pressure proportional tosaid control pressure, and operation support means having normal fluidflow requirements and low pressure requirements varying in a normal lowpressure range for proper full power range operation of said hydrostaticpower transfer means and at times having abnormal higher fluid flowrequirements and lower pressure requirements in a lower abnormal lowpressure range below said normal low pressure range to a minimumabnormal low pressure value; low pressure fluid supply means connectedto and providing said low pressure in said operation support means, andhaving a fluid flow capacity providing said normal fluid flowrequirements of said operation support means in said normal low pressurerange, and operative in response to said abnormal higher fluid flowrequirements to provide said abnormal low pressure range of low pressurevalues; the improvement comprising: control pressure fluid supply meanshaving regulator means operative in response to said high hydrostaticpressure to regulate said control pressure normally in a high controlpressure range proportional to said high hydrostatic pressure; controlmeans connecting said high control pressure supply means to saiddisplacement varying means to vary the relative displacement of saidpump and motor; and said regulator means also being concurrentlyoperative in response to said low hydrostatic pressure decreasing insaid abnormal low pressure range to proportionally reduce said controlpressure to a minimum pressure valve and to proportionally reduce saidhigh hydrostatic pressure.
 2. In a hydrostatic transmission: an input;an output; hydrostatic power transfer means including a pump normallydriven by said input, a motor normally driving said output, a first anda second passage connecting said pump and motor for torque transfertherebetween, with said first passage having high hydrostatic deliverypressure and said second passage having low hydrostatic return pressurewhen torque is transferred from said pump to said motor; fluid operateddisplacement varying means operative in response to control pressure forvarying the relative displacement of said pump and motor to vary thetorque ratio and having the capacity to provide said high hydrostaticdelivery pressure proportional to said control pressure; and operationsupport means having normal fluid flow requirements and low pressurerequirements varying in a normal low pressure range from a normalpressure value to a minimum normal pressure value for proper full poweroperation of said hydrostatic power transfer means, and at times havingabnormal higher fluid flow requirements and lower pressure requirementsin a lower abnormal low pressure range below said normal low pressurerange to a minimum abnormal low pressure value for proper lower poweroperation of said hydrostatic power transfer means; low pressure fluidsupply means having a low pressure source connected to and providingsaid low pressure in said operation support means and having a fluidflow capacity providing said normal fluid flow requirements of saidoperation support means in said normal low pressure range, and operativein response to said abnormal higher fluid flow requirements to providesaid abnormal low pressure range of low pressure values; the improvementcomprising: control pressure fluid supply means having regulator meansoperative in response to said hydrostatic high delivery pressure toregulate said control pressure fluid normally in a high control pressurerange proportional to said high hydrostatic delivery pressure; controlmeans connecting said control pressure fluid supply means to saiddisplacement varying means to vary the relative displacement of saidpump and motor; and said regulator means also being concurrentlyoperative in response to said low hydrostatic pressure decreasing insaid abnormal low pressure range to proportionally reduce said controlpressure to a minimum pressure value and to proportionally reduce saidhigh hydrostatic delivery pressure and drive capacity to substantiallycompletely discontinue drive at said minimum abnormal low pressurevalue.
 3. The invention defined in claim 2, and said operation supportmeans being a charging system having check valves selectively connectingsaid low pressure fluid to the one passage of said first and secondpassages having low hydrostatic return pressure to supply said lowpressure at and above said abnormal minimum pressure value to said onepassage for proper charging without cavitation.
 4. The invention definedin claims 2 or 3, and said operation support means being a lubricationsystem having nozzles to supply fluid for lubrication requiring said lowpressure at and above said minimum abnormal pressure value for properlubrication.
 5. In a hydrostatic transmission: an input; an output;hydrostatic power transfer means including a pump normally driven bysaid input, a motor normally driving said output, a first and a secondpassage connecting said pump and said motor for torque transfertherebetween, with said first passage having high hydrostatic deliverypressure and said second passage having low hydrostatic return pressurewhen torque is transferred from said pump to said motor; and fluidoperated displacement varying means operative in response to controlpressure for varying the relative displacement of said pump and motor tovary the torque ratio and having the capacity to provide said highhydrostatic delivery pressure proportional to said control pressure; lowpressure fluid supply means having a fluid flow capacity providingnormal fluid flow requirements and when providing said normal fluid flowrequirements regulating low pressure at a normal low regulated pressurevalue; charging means connecting said low pressure fluid supply means tosaid first and second passages and normally operative to supply chargingflow requirements to the one of said first and second passages havingsaid low hydrostatic return pressure at the same low pressure value; theimprovement comprising: control pressure fluid supply means havingregulator means for supplying regulated control pressure fluid normallyregulated at a high control pressure value, control means connectingsaid control pressure fluid supply means to said displacement varyingmeans to vary the relative displacement of said pump and motor, and saidregulator means concurrently operative in response to said lowhydrostatic pressure value decreasing in response to above normal fluidflow requirements in a range of pressure values below said normalregulated low pressure value from a less than normal low pressure valuedown to a minimum pressure value to limit said control pressure toproportionally lower values down to zero pressure to proportionallyreduce said high hydrostatic delivery pressure and drive capacity and tosubstantially discontinue drive at said minimum pressure value.
 6. Theinvention defined in claim 5, and said control pressure fluid supplymeans being supplied by said low pressure fluid supply means and, duringregulation, returning overage fluid flow to said low pressure fluidsupply means.
 7. The invention defined in claim 5, and said controlpressure fluid supply means having a first regulator valve responsive tosaid high hydrostatic delivery pressure for regulating said controlpressure at high values proportionately reduced relative to said highhydrostatic delivery pressure value, and a second regulator valveresponsive to said low hydrostatic return pressure and operative tomaintain regulation of said control pressure substantially at said highvalues in a range of normal low pressure values from said normalregulated low pressure value down to a minimum normal low pressurevalue, and for regulation to limit said control pressure toproportionally decreasing values down to zero pressure in response tolow pressure in a range of abnormal low pressure values down to anoperating minimum low pressure value below which said low pressure isinsufficient for charging.
 8. In a hydrostatic transmission: an input;an output; hydrostatic power transfer means including a pump normallydriven by said input, a motor normally driving said output, a first anda second passage connecting said pump and motor for torque transfertherebetween, with said first passage having high hydrostatic deliverypressure and said second passage having low hydrostatic return pressurewhen torque is transferred from said pump to said motor; and fluidoperated displacement varying means operative in response to highcontrol pressure having requirements varying with said high hydrostaticdelivery pressure for varying the relative displacement of said pump andmotor to vary the torque ratio; low pressure supply means for providingregulated low pressure fluid normally regulated at a normal low pressurevalue; supercharge means connecting said low pressure supply means tosaid first and second passages and being operative to supply the one ofsaid first and second passages having said low hydrostatic returnpressure to normally maintain said low pressure in said one of saidfirst and second passages; and lubrication means connecting said lowpressure supply means to said pump and motor for lubrication; theimprovement comprising: high control pressure fluid supply means havingregulator means for providing regulated high control pressure fluidnormally regulated at a high control pressure value proportional to saidhigh hydrostatic delivery pressure to meet high control pressurerequirements; control means connecting said high control pressure fluidsupply means to said displacement varying means to vary the relativedisplacement of said pump and motor; and said regulator meansconcurrently operative in response to said low hydrostatic pressuredecreasing in an abnormal range of pressure values below said normal lowpressure value from a less than normal low pressure value down to aminimum pressure value to proportionally reduce said high controlpressure to zero pressure to proportionally reduce said high hydrostaticdelivery pressure and drive capacity to advise the operator that saidlow pressure is in said abnormal range and discontinue high hydrostaticdelivery pressure and drive at said minimum pressure value.
 9. Theinvention defined in claim 8, and said high control pressure fluidsupply means including regulator valve means connecting overage fluidflow to said low pressure supply means.
 10. The invention defined inclaim 8, and said high control pressure pressure fluid supply meansincluding a first regulator valve responsive to said high hydrostaticdelivery pressure for regulating said high control pressure proportionalto said high hydrostatic delivery pressure and connecting overage fluidflow to said low pressure supply means, and a second regulator valveresponsive to decrease of said low hydrostatic pressure in said abnormalrange to proportionately reduce said high control pressure and tocontinue connecting said overage to said low pressure supply means. 11.The invention defined in claim 10, and said second regulator valveregulating by restricting flow from said first regulator valve, and saidfirst regulator valve continuing said overage fluid flow to said lowpressure supply means.
 12. The invention defined in claim 10, and saidsecond regulator valve regulating by exhaust flow connected to provideoverage fluid flow to said low pressure supply means, and said firstregulator valve remaining open and discontinuing said overage fluidflow.
 13. In a hydrostatic transmission: an input; an output;hydrostatic power transfer means including a pump normally driven bysaid input, a motor normally driving said output, a first and a secondpassage connecting said pump and motor for torque transfer therebetween,with said first passage having high hydrostatic delivery pressure andsaid second passage having low hydrostatic return pressure when torqueis transferred from said pump to said motor; and fluid operateddisplacement varying means operative in response to high controlpressure having requirements varying with said high hydrostatic deliverypressure for varying the relative displacement of said pump and motor tovary the torque ratio; low pressure fluid supply means for providingregulated low pressure fluid regulated at a normal low regulatedpressure value when the fluid supply meets requirements; superchargemeans connecting said low pressure fluid supply means to said first andsecond passages and being operative to supply the one of said first andsecond passages having said low hydrostatic return pressure to normallymaintain said low hydrostatic return pressure at said normal lowregulated pressure value; and lubrication means connecting said lowpressure fluid supply means to said pump and motor for lubrication; theimprovement comprising: high control pressure fluid supply means forproviding regulated high control pressure fluid normally regulated at ahigh control pressure value proportional to said high hydrostaticdelivery pressure; control means connecting said high control pressurefluid supply means to said displacement varying means to vary therelative displacement of said pump and motor; and regulator meansconcurrently operative in response to said low hydrostatic returnpressure decreasing in an abnormal range of pressure values below saidnormal low pressure value down to a minimum pressure for proper chargingand lubrication and to proportionally reduce said high control pressureto zero pressure to proportionally reduce said high hydrostatic deliverypressure and drive capacity to advise the operator of said less thannormal low hydrostatic return pressure and low regulated pressure and todiscontinue drive at said minimum pressure value.
 14. In a cross-drivetransmission having a propulsion drive variable ratio transmission and asteer drive continuously variable ratio hydrostatic transmission, havingan input; an output; hydrostatic power transfer means including a pumpnormally driven by said input, a motor normally driving said output, afirst and a second passage connecting said pump and motor for torquetransfer therebetween, with either of said first and second passageshaving high hydrostatic pressure for power delivery and the other ofsaid first and second passages having low hydrostatic pressure for fluidreturn when torque is transferred from said pump to drive said motor inopposite directions for right and left steer drive; displacement varyingmeans selectively operated by high control pressure for varying thedisplacement of said pump from null position for straight driveselectively to right and left steer displacement positions for right andleft continuously variable ratio steer drive and having the capacity toprovide said high hydrostatic pressure proportional to said high controlpressure; and operation support means including supercharge means withcheck valves connected to supply the one of said first and secondpassages having low hydrostatic pressure; and lubrication meansconnected to supply fluid for lubrication to said hydrostatic powertransfer means and having normal fluid flow and pressure requirementsfor normal minimum to maximum high hydrostatic pressure operation andabnormal higher fluid flow and lower to minimum operating pressurerequirements for proper operation at lower high hydrostatic pressureoperation; low pressure supply means connected to supply low pressure tosaid operation support means and having normal fluid flow and pressurecapacity to meet said normal requirements in a normal range of lowpressure values between a regulated maximum pressure value and a minimumnormal pressure value and inadequate fluid flow capacity to meetabnormal higher fluid flow requirements resulting in a further reductionof low pressure in an abnormal range of lower low pressure values downto a minimum operating pressure value; high control pressure fluidsupply means supplied by said low pressure supply means and includingregulator means providing regulated high control pressure fluid,operative when said low pressure supply means provides said normal rangeof low pressure values for normal regulation in a range of high controlpressure values from a minimum to a maximum varying with said highhydrostatic pressure for proper operation at all hydrostatic pressuresand load capacity, and concurrently operative in response to decreasinglow hydrostatic pressure in said abnormal range to said minimumoperating pressure value to proportionally reduce said high controlpressure value to zero pressure to proportionally reduce saidhydrostatic pressure and load capacity to advise the operator of saidabnormal low pressure by providing decreasing steer capacity with properoperation and then to discontinue drive at said abnormal minimumoperating pressure value to prevent drive with insufficient low pressuresupply to said operation support means.